Study on the Influence of the Mechanical Crushing Process on Low-Temperature Oxidation Characteristics of Coal Samples

Abstract

ABSTRACT In order to study the influence of the mechanical crushing process on the low-temperature oxidation characteristics of coal, the programmed heating experiments of coal samples with different particle sizes were carried out using a programmed heating device. By comparing and analyzing the changes in CO and CO2 emission, cross-point temperature, heat release intensity, and apparent activation energy of coal samples with different particle sizes during temperature heating, the influence of particle sizes on the spontaneous combustion characteristics of coal samples was obtained. On the basis of the infrared spectrum experiment and ESR (electron paramagnetic resonance) experiment of coal samples with different particle sizes, the changes of functional groups and free radicals were further compared, and the deep-seated reasons that the mechanical crushing process affected the spontaneous combustion characteristics of coal were explored. The results showed that with the decrease in particle size, more alkyl side chains are dehydrogenated to produce alkyl radicals during mechanical crushing, and the alkyl radicals are oxidized with oxygen to form more oxygen-containing functional groups. These oxygen-containing functional groups can accelerate the low-temperature oxidation process of coal in the subsequent secondary low-temperature oxidation process, release more heat, and increase the heat release intensity. In the process of mechanical crushing, the coal sample not only changes in physical structure but also changes in chemical structure. With the decrease in particle size of coal samples, more CO and CO2 are produced in the process of low-temperature oxidation of coal, and the time to reach the cross-point temperature is advanced. However, the cross-point temperature and the apparent activation energy decreases, and the spontaneous combustion characteristics of coal are enhanced.